In the art of fire-resistant safes, it is known that one of the important factors in keeping the contents of the safe cool when there is a surrounding fire, is that the composition or filling which makes up the thickness of the wall of the safe includes a large amount of water in various forms or retained in various ways, as for example by absorption or adsorption. The water is valuable in helping to keep the interior of the safe cool, because it absorbs a great deal of heat when passing from liquid phase to vapor phase, since this requires the input of the heat of vaporization. It is therefore desirable, when constructing safes, to use a composition or filling in the wall which contains as much water as reasonably possible.
These principles apply equally to fire-resistant storage boxes, drawers, filing cabinets, or other containers intended to provide some degree of fire protection, and are not limited to safes which are intended to provide burglary protection as well as fire protection. The term fire-resistant container as used hereafter is intended in a generic sense as including safes which may give at least some degree of burglary protection in addition to fire resistance or fire protection, as well as the other mentioned types of containers which may give fire resistance or protection without necessarily providing burglary protection. The principles of the invention apply also to the walls of fire-resistant vaults or rooms permanently built into buildings, and to construction panels which may be utilized in various specialized construction projects, including the construction of walls, roofs, or other parts of special structures where cooling effects or heat-absorbing effects are desired.
In order to retain a large amount of water, various safe manufacturers use a number of known materials, including asbestos, perlite, diatomaceous earth, and vermiculite in the composition used in the filling in the wall of the safe or other container. When vermiculite is used, it has customarily been used, for example, to the extent of about 10 percent by weight of the ingredients making up the filling composition. However, vermiculite is becoming increasingly scarce and increasingly expensive, so that an acceptable substitute for vermiculite is highly desirable. The present invention relates to the discovery of unexpected and valuable properties of certain other materials which can be used satisfactorily to hold the desired amount of water in the filling composition and which will give the composition sufficient strength, enabling the elimination of the vermiculite heretofore thought to be desirable.